1. Field of the Invention
The present invention is related to a mechanism for powering a cylinder poppet valve operating camshaft of an internal combustion engine with a flexible power transmission member driven by the engine's crankshaft.
2. Disclosure Information
Internal combustion engine camshafts have typically been driven either by a gear train, as in heavy duty engines, such as certain diesel engines, or by flexible transmission members such as chains or belts, typically used in gasoline engines and medium duty diesel engines. Gear drives provide the most precise control over the position of the camshaft throughout the engine's useful life. However, gear drives are expensive and generate much more noise than chain or belt drives. On the other hand, although chain and belt drives are less expensive than gear drives, the inevitable wear of chains and belts has caused problems at high mileage with certain engines because mispositioning of the camshaft, as will occur where a tensioner for the chain or belt is applied at only one side of the chain or belt, typically the slack side, will cause phasing of the camshaft with respect to the engine's crankshaft to be changed as the chain or belt wears. This is undesirable for reasons of performance, emissions, fuel economy, and sometimes and, ultimately, engine life in the case of certain engines, wherein a lack of free-wheeling construction means that excessive loss of phase control of the camshaft results in catastrophic destruction of the engine because the pistons of the engine contact the valves at top dead center.
A camshaft drive system according to the present invention provides accurate control of the camshaft phasing, in the context of a less expensive belt or chain system, using hardware which is available at a reasonable cost.